The present invention relates to the art of signal generators and, more particularly, to improvements in unipolar rotational speed transducers.
Unipolar or homopolar generators are of course well known in connection with the generating of electrical signals. In one form of such generators, a cylinder of conductive material such as copper is rotated about the axis of the cylinder and in a magnetic field which is radial with respect to the axis of rotation. A potential difference is generated axially of the cylinder in response to rotation of the cylinder in the magnetic field, whereby an output signal indicative of rotor speed can be obtained such as through the use of brush contacts at axially opposite ends of the cylinder. In another form, a disc of conductive material such as copper is rotated about an axis perpendicular to the plane of the disc and in a magnetic field which is parallel to the axis of rotation. Accordingly, a potential difference is generated radially of the rotor disc, whereby an output signal proportional to the speed of rotation of the disc can be obtained such as through brush contacts which are generally connected respectively to the rotor shaft and the radially outer periphery of the rotor disc.
The approach in connection with many signal generators heretofore provided has been to produce a device having a high voltage output signal. Such designs have been dimensionally large and structurally complex, resulting in a high inertia operation, and have required a considerable number of component parts which adds to the expense of the generators both from the standpoint of the number of parts and the assembly time required with respect thereto. In addition to such high voltage signal designs, efforts have been made to provide physically smaller signal generators, some of which designs have included the use of permanent magnets to provide the magnetic field. These designs generally have a low current output and, while promoting a smaller size than the high current designs, are not economical to produce and have not overcome the problems of structural complexity and an excessive number of component parts to be assembled and structurally interrelated with one another. Moreover, while promoting a smaller size, such designs still have a high inertia characteristic in proportion to the size thereof. Furthermore, both such high power and low power D.C. signal generators heretofore provided have included windings and commutating arrangements which produce a ripple in the output signals therefrom and a low signal to noise ratio, both of which are undesirable. Especially in connection with designs toward miniaturizing the physical size of such generators, the structures often require precision parts and extreme care in assembly in order to provide stability against undesirable relative displacements between the component parts of the character which affect efficiency of operation and uniformity with respect to the output signal. One problem in particular in connection with miniaturization of the unipolar generator is the positioning of the brush elements so as to optimize uniformity of the output voltage signal. More particularly in this respect, uniformity of the output signal is optimized by positioning the brush elements outside the magnetic field and, heretofore, the structural arrangements of the component parts of generator units would require enlargement rather than reduction of the overall unit size in order to achieve such positioning of the brush elements.